Conventionally known is an automatic open-close device for automatically opening and closing slider windows (Patent reference 1, for example). An automatic open-close device disclosed in Patent reference 1 is equipped with a rack secured to a window, a pinion which meshes with the rack, and a motor having an output shaft to which the pinion is secured. To a window frame to which a window is openably and closeably mounted, a support case is mounted; to the support case, a motor is secured. In this automatic open-close device, as the motor is driven to turn the pinion, the window to which the rack is secured opens and/or closes.